Filtering elements of an array with elements of another array in Perl 6

Question

I want to filter elements of @array which begin with elements of @search:

my @array = "aaaaa" .. "fffff";
my @search = "aaaa" .. "cccc";
.put for @array .grep: /^ @search /;

The problem is it takes 19 seconds. So, I 'precompile' the regex for grep, and the whole program looks like this:

my @array = "aaaaa" .. "fffff";
my @search = "aaaa" .. "cccc";

my $search = "/@search.join('|')/".EVAL;

.put for @array .grep: * ~~ /^ <$search> /;

Now it takes 0.444s.

The question: is there a built-in Perl 6 method to do such things? Something like inserting a junction into a regex...

Answer 1

my @array = "aaaaa" .. "fffff";
my @search = "aaaa" .. "cccc";
my $join = @search.join('|');
my $rx = rx{ ^ <{$join}> };

@array.grep( * ~~ $rx ).map( *.put )

You need to create the join string separately of it will evaluate the array join for each match. But the basically gives you what you want without using EVAL.